Mind the gap junction.

Top Line: Radiation may fix not only refractory heart arrhythmias but also hearts.

The Study: Ok, stay with us. The cardiac SBRT pioneers from Wash U are suggesting that the commonly used regimen of 25Gyx1 for cardiac ablation is not actually killing heart cells as anticipated, as there is no appreciable post-radiation rise in troponin levels, but instead by “healing” heart cells. Say what? The intention of any form of cardiac ablation is to destroy cardiac muscle full thickness where there is currently partial thickness damage allowing for aberrant conduction pathways. What has been observed after SBRT, however, is that arrhythmias resolve in the matter of days—not on the timeline of months expected from radiation-induced cardiac cell death. Indeed, post-radiation cardiac MR images demonstrate little fibrosis development, at least anywhere in the timeframe of arrhythmia reduction. So what is responsible for its impressive efficacy? This basic science work expands our understanding of healing rays. In murine models, cardiac radiation actually reprograms cardiac cells by upregulating things like connexin 43, the major subunit of the ventricular gap junction that allows for diffusion of charge, with a measurable clinical outcome of increased conduction velocities in both scarred and normal heart muscle. Maybe the TARGIT group was onto something.

TBL: Once again, the radiobiologic outcomes of ablative radiation are farther-reaching than initially imagined. | Zhang, Nat Commun 2021